Bulk acoustic wave filter and a method of frequency tuning for bulk acoustic wave resonator of bulk acoustic wave filter
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Solution Overview
Problem
The complexity in fabricating bulk acoustic wave resonators with precise frequency tuning is increased by adjusting the thickness difference of top electrodes, which can affect the performance characteristics and is economically challenging.
Innovation Solution
A method involving forming sacrificial structure mesas with height differences on a substrate, followed by the deposition of insulating and piezoelectric layers, and chemical-mechanical planarization to create cavities, allowing for precise frequency tuning by adjusting the height difference of these mesas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the thickness difference of top electrodes is adjusted to tune resonance frequency difference, then frequency tuning is achieved, but device complexity and manufacturing complexity increase
Solution Approach 1:
The patent introduces a sacrificial layer as an intermediary substance that enables frequency tuning without requiring complex electrode thickness variations. The sacrificial layer is deposited to different thicknesses in different regions, then selectively removed to create air gaps that tune the resonance frequency. This mediator approach simplifies the final structure compared to directly creating unequal electrode thicknesses.
Solution Approach 2:
The patent performs preliminary deposition of the sacrificial layer to the full thickness before selective removal. This preliminary action establishes a uniform base layer that is then selectively reduced in certain areas to create the desired air gaps. This approach is simpler than attempting to deposit material to different thicknesses from the beginning.
2Manufacturing precision
If the thickness difference of top electrodes is adjusted to tune resonance frequency difference, then frequency tuning is achieved, but manufacturing process complexity increases
Solution Approach 1:
The sacrificial layer serves as a temporary intermediary that simplifies manufacturing. Instead of directly creating complex electrode thickness patterns, the process uses a uniform sacrificial layer deposition followed by selective removal. This two-step approach is more manufacturable than direct precision thickness control of electrodes.
Solution Approach 2:
The patent changes the parameter being controlled from electrode thickness to sacrificial layer thickness and air gap size. This parameter substitution makes the manufacturing process easier because depositing uniform thick layers and selectively removing portions is simpler than precisely controlling thin electrode thickness variations across different regions.
3Manufacturing precision
If structure differences between resonators are increased to achieve frequency tuning, then resonance frequency difference is achieved, but performance characteristics are affected
Solution Approach 1:
The sacrificial layer acts as a temporary structure that enables frequency tuning without permanently altering the resonator performance characteristics. By using the sacrificial layer to define air gaps rather than creating permanent structural differences in the resonators themselves, the patent maintains better performance consistency while achieving the desired frequency tuning.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enhances the performance and reduces economic considerations by allowing precise tuning of resonance frequencies without compromising the characteristics of the bulk acoustic wave resonators.
Implementation Method 1
polishing the sacrificial layer by a chemical-mechanical planarization (CMP) process
Implementation Method 2
forming a piezoelectric layer on the bottom electrode layer
Data Source
AI summary
A method for forming cavity of bulk acoustic wave resonator comprising following steps of: forming a sacrificial epitaxial structure mesa on a compound semiconductor substrate; forming an insulating layer on the sacrificial epitaxial structure mesa and the compound semiconductor substrate; polishing the insulating layer by a chemical-mechanical planarization process to form a polished surface; forming a bulk acoustic wave resonance structure on the polished surface, which comprises following steps of: forming a bottom electrode layer on the polished surface; forming a piezoelectric layer on the bottom electrode layer; and forming a top electrode layer on the piezoelectric layer, wherein the bulk acoustic wave resonance structure is located above the sacrificial epitaxial structure mesa; and etching the sacrificial epitaxial structure mesa to form a cavity, wherein the cavity is located under the bulk acoustic wave resonance structure.